Limitations of endoscopic ablation in Barrett's esophagus

An endoscopic approach providing near-infrared laser-induced coagulation with accurate depth limits

This article investigates an endoscopic approach that utilizes negative pressure to achieve laser-induced thermal coagulation limited to the esophageal wall's mucosal and superficial submucosal layers. The study was built upon a series of studies combining numerical simulation based on the Monte-Carlo technique and ex vivo porcine tissue experiments, including apparatus design and histology analysis. An endoscopy apparatus was developed using 3D printing to validate the tissue stretching-based approach. A fiber-pigtailed diode was used as the near-infrared source, emitting 208.8 W/cm2 laser irradiance at 1.5 μm. Simulation results suggested that the approach successfully created a local heat well to prevent residual thermal effects (>65°C) from penetrating the deeper submucosal layer. Histology analysis of ex vivo tissues showed that at a fluence of 5.22 kJ/cm2, the depth of thermal coagulation was reduced by half compared to the control. With further preclinical studies, including endoscopy apparatus design, the approach can be applied to the larger esophageal surface.

Guide mapping for effective superficial photothermal coagulation of the esophagus using computer simulations with ex vivo sheep model validation study

OBJECTIVES

The transfer and widespread acceptance of laser-induced thermal therapy into gastroenterology remain a topic of interest. However, a practical approach to the quantitative effect of photothermal injury in the esophagus needs further investigation. Here, we aim to perform computer simulations that simulate laser scanning and calculate the laser-induced thermal damage area. The simulation engine offers the results in a guide map for laser coagulation with a well-confined therapeutic area according to laser irradiance and surface scanning speed. The study also presents validation experiments that include histology analyses in an ex vivo sheep esophagus model.

METHODS

The simulation engine was developed based on the Monte-Carlo method and the Arrhenius damage integral. The computational model mimicked laser scanning by shifting the position of the calculated heat source in the grating system along the axis to be scanned. The performance of the simulations was tested in an ex vivo sheep esophagus model at a laser wavelength of 1505 nm. Histological analysis, hematoxylin-eosin staining, light microscope imaging, and block-face scanning electron microscopy were used to assess thermal damage to the tissue model.

RESULTS

The developed simulation engine estimated the photothermal coagulation area for a surface scanning speed range of 0.5-8 mm/second and laser power of up to 0.5 W at a 0.9-nm laser diameter in a tissue model with a volume of 4 × 4 × 4 mm³ . For example, the optimum laser irradiation for effective photothermal coagulation in the mucosa and superficial submucosa depths was estimated to be between 16.4 and 31.8 W/cm² , 23.2 and 38.1 W/cm² at 0.5 and 1 mm/second, respectively. The computational results, summarized as a guide map, were directly compared with the results of ex vivo tissue experiments. In addition, it was pointed out that the comparative theoretical and experimental data overlap significantly in terms of energy density.

CONCLUSIONS

Our results suggest that the developed simulation approach could be a seed algorithm for further preclinical and clinical trials and a complementary tool to the laser-induced photothermal coagulation technique for superficial treatments in the gastrointestinal tract. In future preclinical studies, it is thought that the simulation engine can be enriched by combining it with an in vivo model for different laser wavelengths.